1. Field of Invention
The present invention relates generally to passenger lifts of the type having a lift platform that is movable between a generally vertical stowed position in a motor vehicle, a deployed horizontal position at the height of the vehicle floor, and a lowered position resting on the ground, for transporting a passenger occupying a scooter, a wheelchair or otherwise between the vehicle and the ground.
More particularly, the invention relates a passenger lift of the above type but which is adapted for two-speed operation, with one speed being used for deployment and retraction of the lift platform from and to the stowed position, and with the second speed being used to raise and lower the lift platform and passenger between the vehicle and the ground.
2. Description of Prior Art
Passenger lifts of the subject type typically utilize a parallelogram-type linkage assembly to maintain the lift platform parallel to the ground while raising and lowering a passenger. For example, Farsai, U.S. Pat. No. 5,433,581, utilizes a hydraulically driven chain and sprocket system with a parallelogram-type linkage to raise and lower the lift platform. Saucier et al., U.S. Pat. Nos. 5,944,473 and 5,605,431 utilize hydraulic cylinder actuated parallelogram linkages to effect the different motions of stowing and deploying, and raising and lowering the lift platform. And Rindgahl et al, U.S. Pat. No. 5,672,041 utilizes a mechanically actuated parallelogram linkage.
Many early passenger lifts were single speed lifts, operating at the same speed when moving between the stowed position and the deployed position at the height of the vehicle floor, and between the vehicle floor and ground level. In order to keep impact and vibrations to within reasonable limits during deployment and retraction of the lift platform, the speed of such passenger lifts is typically relatively slow. However, this results in relatively slow movement of the platform between the vehicle and the ground. Alternately, the operating speed of the lifts have been increased for desired raising and lowering of the lift platform, resulting is excessive impact and vibration during deployment and retraction operations. In either event, such single speed lifts generally exhibit certain undesirable motion characteristics either during deployment and retraction, and/or during raising and lowering of the lift platform. Therefore, in order to provide for relatively slow deployment and retraction of the lift platform, and reasonably fast raising and lowering of the platform, passenger lifts now typically include provision for at least two-speed operation.
Numerous power operating and control mechanisms for actuating and controlling the speed of movement of the subject type of passenger lift, including to establish two-speed operation, are known in the prior art. For example, Farsai utilizes hydraulic fluid flow-control for speed control of lowering the platform via gravity, and a cam-roller configuration adjustment for refinement of the deployment and retraction speed. The patents to Saucier et al. utilize a complicated flow-control schemes to control the speed of the passenger lift. Other prior passenger lifts utilize other electrical and/or flow-control arrangements to effect two-speed or multi-speed operation, including recent use of microprocessors for speed control. However, such arrangements tend to be relatively complicated, and therefore, relative expensive and correspondingly less reliable. Thus, there is a need for an improved two-speed passenger lift that is relatively simple, more reliable and less expensive than prior speed control arrangements.
In addition, it is desirable to provide currently installed single-speed passenger lifts with two-speed operation to achieve more desirable operating characteristics. Therefore, to provide such lifts with the advantages of two-speed operation, it is desirable that the speed-control of an improved passenger lift be provided in a form suitable for retrofitting onto single-speed lifts.